Modular structures, meaning structures comprised of identical repeated components, provide significant construction advantages as components can be prefabricated and mass-produced. Modular design and construction can reduce the overall project cost and project schedule. Modular approaches can be used for a wide variety of structures, including bridges and buildings.
Modular bridges are comprised of prefabricated components or panels that can be rapidly assembled on a site. Existing modular or panelized steel bridging systems (e.g., Bailey, Acrow, Mabey-Johnson) consist of rigid rectangular steel panels that are connected by pins and are arranged in a longitudinal configuration to form a girder-type bridge. They have also been used in alternative configurations to construct bridge piers, suspension bridges, movable bridges, and buildings, as well as for temporary formwork or scaffolding for construction. These modular bridges were developed to serve needs in rapid construction in war, but have also been widely used in emergencies and disasters. Early attempts at modular bridging included the Callender-Hamilton Bridge which was comprised of individual steel members bolted together on site. These were later replaced by the Bailey Bridge system, and its derivatives, which featured rigid panels connected by pins that were easier and faster to erect.
These prior art systems feature rigid, rectangular modules (typically 3.05 m (10 ft) in length, see for example a Bailey panel 10 in FIG. 1A) which are connected longitudinally to form girder-type bridges. Versatility of these existing systems is achieved by stacking modules vertically and/or transversely to reach longer spans (up to 61.0 m to 91.4 m (200 to 300 ft)) and/or higher load capacity (see for example the double-triple configuration—meaning two modules stacked transversely and three modules stacked vertically—of a Bailey system 12 in FIG. 1B). However, the material efficiency (quantified in this disclosure as span squared per weight) of these longer, stacked configurations is limited since (1) material is placed at or near the neutral axis which contributes little to the strength of the system in a bending dominant girder configuration and (2) stacking is not varied along the span despite varying moment and shear demands. This disclosure addresses at least these limitations by developing a new type of module which is capable of varying depth based on demand: an adjustable module which can form variable depth bridges.
Other examples of portable bridges include U.S. Pat. No. 4,628,560 to Merton L. Clevett which describes “transportable bridge structures including pantograph or lazy tong trusses with insertable deck sections to provide parallel tracks or walkways.” (Col. 1:12-15) This patent, issued in Dec. 16, 1986, describes “a rapid deployment bridge structure of the foregoing character which is light in weight, easily erected and which floats in water” and “is adjustable in length prior to deployment and erection.” (Col 1:33-35, 39-41)